New master/slave scheme for semi-1.14.x ports. Update master port to emacs21.
Update slave ports to stub port: semi-emacs20, semi-xemacs21-mule. Does not
support semi-emacs(19) and semi-mule for semi-1.14.x or later. Change some
style.

Change PKGDIR from pkg/ to . Also fix places where ${PKGDIR} is spelled out
(many of which are ${PKGDIR}/MESSAGE -> ${PKGMESSAGE} type fixes that
shouldn't have been necessary) and the string "/pkg/" appear.